If you want a very simple tool, I'd say SuperSU is the go-to tool. In most custom ROMs I tried, yet, it even is pre-installed, because it is so small and simple.
However, in case you want a bit more, and I am talking about easy to install plugins, fixes and root-apps here, then there also is Magisk. As far as I know it is based on SuperSU, but offers a lot more functionality, and if you want to get things working quickly and easily, it often is the best alternative to installing by recovery.